BIOLOGY PRELIMINARY NOTES
KIARA DURKIN
DNA – THE CODE OF LIFE
Nucleic acids control protein synthesis
Nucleic acids found in cells:
1. DNA (Deoxyribonucleic acid)
• Where is DNA found?
- Nucleus of all cells
- Important part of chromosomes
*Chromatin: chromosomal material made up of DNA, RNA and histone proteins as found in a non-
dividing cell
• What is extranuclear DNA?
- Small amounts of DNA found outside of nucleus: mitochondria & chloroplasts
• Composition of DNA - nucleotides
- Sugar molecule – deoxyribose
Each nucleotide
- Phosphate molecule
is composed of
- Nitrogenous base: adenine, cytosine, guanine, thymine
- Bases = foundation of genetic code (instruct cells to synthesise proteins)
• How is the double helix made up?
- Outer strands = alternating sugar + phosphate molecules
- Rungs formed by pairs of bases (attached by weak hydrogen bonds)
- Bases attached to sugar molecules
• How do these base pairs link up?
- Adenine bonds with thymine/ uracil (2 H bonds)
- Guanine bonds with cytosine (3 H bonds)
• How are base pairs classified?
- Purines (two fused rings of H, N, C atoms) – guanine, adenine
- Pyrimidines (one ring of H, N, C atoms) – thymine, cytosine, uracil
- Base pairs = 1 purine + 1 pyrimidine
• How do organisms differ?
- The sequence in which the nucleotides are strung together
- Sequences in certain sections of DNA differ in each human (except identical
twins)
- Sequence of nucleotides determines genetic code of organism
• Role of DNA
- Carry hereditary information (genes) in each cell
- Provide blueprint for organisms’ development by coding for protein synthesis
- Replicate to copy genetic information in each daughter cell during cell division =
genetic code passed on through each generation
• What is non-coding DNA?
- DNA that does not code for protein synthesis
- Exons = coding; introns = non-coding
- Form RNA molecules
• Extraction of DNA from organic matter
- Release as much DNA as possible
- Minimise DNA degradation
- Be efficient (cost, labour, time, supplies)\
, Replication
The process of making a new identical DNA molecule from an existing one
• Takes place during interphase
• How does replication occur?
- Catalysed by enzyme DNA polymerase
- Double helix unwinds
- Weak hydrogen bonds holding pairs break; 2 strands part
- Each base is exposed
- Free nucleotides in nucleoplasm bond to exposed matching base
- One DNA double helix becomes 2 identical helices
- Both daughter molecules twist to form helix which wraps around histone
• Why is replication necessary?
- DNA needs to replicate itself to ensure genetic code passed on to each daughter
cell
2. RNA (Ribonucleic acid)
• Structure of RNA
- Consists of nucleotides
- Single strand, shorter than DNA
- Sugar is ribose, not deoxyribose
- Uracil replaces thymine
• Function of RNA
- Carries instructions from DNA to ribosomes where protein synthesis occurs
• Similarities between DNA and RNA
- Both made up of polymers and nucleotides (sugar, phosphate, nitrogen base)
- Both responsible for protein synthesis
Mitochondrial DNA (mtDNA)
• Double stranded
• Ring shaped
• Comes from egg cell (oocyte) = maternal
• Has its own genome that codes for enzymes, rRNA and tRNA
• Essential for functioning of mitochondria + code for enzymes that control cellular
respiration
• Tracing genetic links
- During fertilisation, sperm only enters egg cell, no other organelle
- All other organelles are from mother
- mtDNA passed on = establishes direct maternal genetic line
- mtDNA mutates occasionally = nucleotide replaced, site of mutation = marker
- mtDNA profile of 2 sets of these markers made:
1. If both profiles are very similar = organisms closely related
2. If both profiles different = organisms diverged during evolution
- Markers mapped through generations; enables researchers to trace
matrilineages (lineages through females) back to ancestry of human groups/
individuals
• What is mtDNA testing?
- Scrape of tissue from cheek sent to laboratory of genetic genealogy
- Compared with existing samples/ reference sample (Cambridge Reference
Sequence – CRS) – source of information of mtDNA found in people of European
descent
KIARA DURKIN
DNA – THE CODE OF LIFE
Nucleic acids control protein synthesis
Nucleic acids found in cells:
1. DNA (Deoxyribonucleic acid)
• Where is DNA found?
- Nucleus of all cells
- Important part of chromosomes
*Chromatin: chromosomal material made up of DNA, RNA and histone proteins as found in a non-
dividing cell
• What is extranuclear DNA?
- Small amounts of DNA found outside of nucleus: mitochondria & chloroplasts
• Composition of DNA - nucleotides
- Sugar molecule – deoxyribose
Each nucleotide
- Phosphate molecule
is composed of
- Nitrogenous base: adenine, cytosine, guanine, thymine
- Bases = foundation of genetic code (instruct cells to synthesise proteins)
• How is the double helix made up?
- Outer strands = alternating sugar + phosphate molecules
- Rungs formed by pairs of bases (attached by weak hydrogen bonds)
- Bases attached to sugar molecules
• How do these base pairs link up?
- Adenine bonds with thymine/ uracil (2 H bonds)
- Guanine bonds with cytosine (3 H bonds)
• How are base pairs classified?
- Purines (two fused rings of H, N, C atoms) – guanine, adenine
- Pyrimidines (one ring of H, N, C atoms) – thymine, cytosine, uracil
- Base pairs = 1 purine + 1 pyrimidine
• How do organisms differ?
- The sequence in which the nucleotides are strung together
- Sequences in certain sections of DNA differ in each human (except identical
twins)
- Sequence of nucleotides determines genetic code of organism
• Role of DNA
- Carry hereditary information (genes) in each cell
- Provide blueprint for organisms’ development by coding for protein synthesis
- Replicate to copy genetic information in each daughter cell during cell division =
genetic code passed on through each generation
• What is non-coding DNA?
- DNA that does not code for protein synthesis
- Exons = coding; introns = non-coding
- Form RNA molecules
• Extraction of DNA from organic matter
- Release as much DNA as possible
- Minimise DNA degradation
- Be efficient (cost, labour, time, supplies)\
, Replication
The process of making a new identical DNA molecule from an existing one
• Takes place during interphase
• How does replication occur?
- Catalysed by enzyme DNA polymerase
- Double helix unwinds
- Weak hydrogen bonds holding pairs break; 2 strands part
- Each base is exposed
- Free nucleotides in nucleoplasm bond to exposed matching base
- One DNA double helix becomes 2 identical helices
- Both daughter molecules twist to form helix which wraps around histone
• Why is replication necessary?
- DNA needs to replicate itself to ensure genetic code passed on to each daughter
cell
2. RNA (Ribonucleic acid)
• Structure of RNA
- Consists of nucleotides
- Single strand, shorter than DNA
- Sugar is ribose, not deoxyribose
- Uracil replaces thymine
• Function of RNA
- Carries instructions from DNA to ribosomes where protein synthesis occurs
• Similarities between DNA and RNA
- Both made up of polymers and nucleotides (sugar, phosphate, nitrogen base)
- Both responsible for protein synthesis
Mitochondrial DNA (mtDNA)
• Double stranded
• Ring shaped
• Comes from egg cell (oocyte) = maternal
• Has its own genome that codes for enzymes, rRNA and tRNA
• Essential for functioning of mitochondria + code for enzymes that control cellular
respiration
• Tracing genetic links
- During fertilisation, sperm only enters egg cell, no other organelle
- All other organelles are from mother
- mtDNA passed on = establishes direct maternal genetic line
- mtDNA mutates occasionally = nucleotide replaced, site of mutation = marker
- mtDNA profile of 2 sets of these markers made:
1. If both profiles are very similar = organisms closely related
2. If both profiles different = organisms diverged during evolution
- Markers mapped through generations; enables researchers to trace
matrilineages (lineages through females) back to ancestry of human groups/
individuals
• What is mtDNA testing?
- Scrape of tissue from cheek sent to laboratory of genetic genealogy
- Compared with existing samples/ reference sample (Cambridge Reference
Sequence – CRS) – source of information of mtDNA found in people of European
descent
